NEW ORLEANS (CN) – Although no evidence links it to the Deepwater Horizon oil spill, this year’s “dead zone” in the Gulf of Mexico has doubled since last year, and researchers say it might be even larger than mapped.
The dead zone, which stretches from the mouth of the Mississippi River into Texas, is created by low levels of oxygen in water, known as hypoxia.
According to the Louisiana Universities Marine Consortium’s website, the Gulf’s dead zone is the largest dead or “hypoxic” zone currently affecting the United States, and the second largest worldwide.
The low-oxygen area is linked to high concentrations of nutrients found in agricultural fertilizers such as nitrogen and phosphorous as well as other nutrients carried into the Gulf by the Mississippi River.
Scientists with the Louisiana Universities Marine Consortium announced Monday that this year’s dead zone stretches 7,722 square miles across Louisiana’s coast into Texas waters – an area the size of Massachusetts.
That finding matches predictions made earlier this year by Louisiana State University biologist Eugene Turner, who predicted a range of over-oxygenated water averaging 7,776 square miles based on measurements of nutrients carried by the Mississippi River this spring.
The dead zone is in the Mississippi River Delta along Louisiana’s vast coastline. This area of the country hosts some of world’s most diverse ecosystems, and provides 16 percent of U.S. fisheries and habitat for 70 percent of migratory birds in all of North America.
Though the dead zone is in the Gulf of Mexico, the nutrients and contamination that cause the low oxygen levels in water are largely the result of accumulated nutrients in sediment coming from across the Midwest, from areas along the Mississippi River and rivers that flow into the Mississippi.
Once the nutrients land in the Gulf of Mexico, they feed blooms of springtime and summertime algae at the surface. As the algae sink to the bottom, die and decompose, they use up the oxygen in the water.
Oxygen levels that are lower than 2 parts per million can kill organisms in the Gulf floor sediment that are food sources for larger oceanic species, such as fish and shrimp.
The Mississippi River/Gulf of Mexico Watershed Nutrient Task Force wants to reduce the average size of dead zones to 1,900 square miles by 2015.
Its plan involves getting urban sewage systems and septic tank owners to reduce emissions, and convincing agricultural sources to lower farm fertilizer use and develop grassy areas on the edges of farmland to soak up excess nutrients before they seep into the river.
But several environmental organizations, scientists and even the Environmental Protection Agency’s inspector general say efforts on a voluntary basis will not move quickly enough to sustain the Gulf against rapid increase in its annual dead zone.
Because regulation has so far been left up to individual states, in August 2009 the EPA Office of Inspector General recommended implementing firm standards for the amount of nutrients allowed in the Mississippi and other waterways.
“Critical national waters such as the Gulf of Mexico and the Mississippi River require standards that, once set, will affect multiple upstream states,” according to the agency’s report. “These states have not yet set nutrient standards for themselves; consequently it is EPA’s responsibility to act.”
Nancy Rabalais, executive director of the Louisiana Universities Marine Consortium said Monday it is still unclear what effect, if any, the oil spill has had on the size of this year’s dead zone.